Conduit of adjustable stiffness

ABSTRACT

An electrical connector including a flexible armored sheath having an insulated conductor threaded therethrough and electrically connected between a plug unit and a breech cap which is adapted for applying a firing signal to a pyrotechnic cartridge and which has flanged spring pins formed to function both as ground contacts and as spent cartridge extracting means. A braided sheath encircles the armored sheath and is mechanically connected at one end to the breech cap and at the other end through a turnbucklelike sheath stretching assembly to the plug unit. The stretching assembly enables the braided sheath to be longitudinally stretched so that it tightly grips the armored sheath and forms therewith a more rigid conduit.

I Unlted States Patent 13,569,912

[72] Invent rs Carl A- D mm 1,651,022 11/1927 Fulton 285/114 Upper BlackEddy; 2,750,210 6/1956 Trogdon et a1. 285/305X Albert C. Eichmann,Huntingdon Valley; FOREIGN PATENTS William phihdelph'a 1,028,194 4/1968Germany 285/91 [21] 828902 602 547 8/1934 German 285/114 Filed y 29,1969 y [45] Patented Mar. 9, 1971 Primary Examiner-Dave W. Arola [73]Assignee the United States of America as represented Attorneys-Edgar J.Brower, Henry Hansen and B. Frederick by the Secretary of the NavyBuchan, Jr. 1 Division of Ser. No. 719,629, Patent No. 3,504,592, Apr.8, 1968 ABSTRACT: An electrical connector including a flexible ar- [54]CONDUIT 0F ADJUSTABLE STIFFNESS mored sheath having an insulatedconductor threaded 2 Claims, 5 Drawing Figs therethrough andelectrlcally connected between a plug umt 1 and a breech cap WhlCh 1sadapted for applying a firing signal [52] U.S. Cl 339/101, to apyrotechnic cartridge and which has flanged spring pins 174/168, 285/91,285/114, 285/3 formed to function both as ground contacts and as spentcarllgt. Cl. t idg ext a ti g means A braided sheath encircles the at.[$0] Fleld of Search 285/ 305, meted Sheath and is mechanicallyconnected at one end to the v 1141913441235; 138/129; 285/91i339/101;174/168 breech cap and at the other end through a turnbucklelike sheathstretchin assembl to the lu unit. The stretchin as- [56] References andsembly enables the bra ided 811 2351 to be longitudisally UNITED STATESPATENTS stretched so that it tightly grips the armored sheath and forms3,199,541 8/1965 Riuhitellim therewith a more rigid conduit.

CONDUIT OF ADJUSTABLE STIFFNESS CROSS-REFERENCES TO RELATED APPLICATIONSThis application is a division of application Ser. No. 719,629 filedApr. 8, 1968 now US. Pat. No. 3,504,592.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION Pyrotechnically actuated bomb racks arefrequently rendered inoperable by reason of the electrical failure of aconnector which terminates at one end in a breech cap adapted forapplying a detonation signal to a pyrotechnic cartridge carried in anejector assembly. The connector needs to be flexible and cannot besecured to adjacent structure of the bomb rack because the breech capmust be removed to load cartridges. Flexible connectors are subjected tobuffeting by air turbulence during flight which causes the connector tovibrate with consequential weakening and eventual severance of theelectrical conduction path.

SUMMARY OF THE INVENTION It is the general purpose of this invention toprovide an improved conduit for an electrical connector which assuresthat a good electrical conduction path will be maintained and which canbe made stiff enough to resist the deleterious effects of buffeting byair turbulence and yet does not interfere with easy disconnection of thebreechv cap from its associated pyrotechnic ejector assembly. Briefly,this is accomplished by providing a flexible armored sheath adapted tocarry an untensioned length of conductor electrically interconnectingthe breech cap and an anchor and plug unit; by providing a stretchablesheath which encases the flexible armored sheath and is mechanicallyconnected in a linkage between the breech cap and the anchor unit; andby providing adjustable stretching devices, such as a breechcap couplingor a turnbuckle assembly interconnected between an end of thestretchable sheath and the cap or the anchor unit, for longitudinallystretching the encasing sheath and causing it to grip the periphery ofthe armored sheath and form a more rigid conduit which can withstandintense air turbulence.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents a side view partiallyin cross section of a connector according to the invention;

FIG. 2 represents an enlarged view in longitudinal cross section of aportion of a flexible armored sheath included inthe connector of FIG. 1;

FIG. 3 represents an enlarged side view of a disengaged ground contactpin included in the connector of FIG. 1;

closing plate 14 through which protrude force fit, flanged groundcontact pins 15, hereinafter more fully described, and a spring-loadedprimary contact 16. The pins 15 and 16 establish good electrical contactwith a pyrotechnic cartridge 17 which is received within the barrel 13and is of the type detonated by an electrical firing signal. The tubularcoupling 12 may include a plurality of key slots (not shown)longitudinally extending from the barreladjacent end of the coupling 12and sized to receive a spring-loaded key (not shown) for preventingrelative rotation of the coupling 12 and the barrel 13.

The breech cap 11 also includes a flanged, stainless steel pressure dome18 which is welded to and closed by the plate 14 and which, among otherthings, sandwiches the ground contact pins 15 in position. The rotatablecoupling 12 is retained adjacent the flanged end of the dome 18 by ametal snap ring 12a seated in a peripheral groove formed in the dome 18.A flexible, insulated conductor 19 which extends into the dome 18 has astranded signal lead (not shown) electrically connected at one end withthe primary contact 15 and has an inner ensheathing, braided groundshield (not shown) insulated from the lead and mechanically andelectrically connected to the dome 18. The other end of the conductor 19extends into a hollow anchor unit 20 and is electrically connected to aplug 21 which protrudes from the anchor unit 20. The anchor unit 20 isrigidly connected as by bolts (not shown) with a framing structure 22rigidly connected to the bomb rack after insertion of the plug 21 intoan aperture 22a formed in the structure 22 for establishing anelectrical connection with a recessed receptacle 23 mounted in theaperture 22a. The receptacle 23 is electrically connected with a controlunit (not shown) which provides the electrical firing signal to beapplied by the cap 11 to the cartridge 17.

The conductor 19 extends through an aperture formed in 4 the end of thedome 18 remote from the barrel l3 and is FIG. 4 represents an end viewof the pointed end of the pin I of FIG. 3; and

FIG. 5 represents an enlarged cross-sectional view of the pin inpiercing engagement with a cartridge casing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, theconnector 10 terminates at one end in a breech cap 11 generally of thetype described in US. Pat. application Ser. No. 700,603, now US. Pat.No. 3,490,332, filed Jan. 25, 1968, by Carl A. Damm for Breech Cap forApplying Signals to Explosive Cartridges." The breech cap 11 includes arotatable, inwardly flanged coupling 12 which is connected to a barrel13 of an ejector assembly (not shown) such as that generallydescribed'in US. Pat. No 3,036,852 to C. W. Mullison, issued May 29,1962, and in US. Pat. application, Ser. No. 657,738, filed Jul. 21,1967, by Carl A. Damm for Ejector Assembly with Lockable Store-EngagingPresser Foot." The breech cap further includes an apertured breechthreaded through a tubular boss 30 which is fixed to and protrudes fromthe dome 18. The extended end of the boss 30 terminates in a radiallyextending flange 31 and has a coaxial bore 30a extending thereinto whichis sized to slidingly receive an end of a flexible armored sheath 32through which the conductor 19 is threaded. The other end of sheath 32is slidingly received by a turnbucklelike stretching assembly 40 throughwhich the conductor 19 is threaded.

The stretching assembly 40 includes a coaxially apertured, internallythreaded adjusting bolt 41 which has a hexagonal head and oppositelydirected, similarly pitched, external threads and which is threadablyengaged by the anchor unit 20. One end of a coaxially apertured fitting42 is threaded into the bolt 41. The other end of the fitting 42terminates in a flanged boss 43 having a coaxial bore 43a extendingthereinto which is sized to slidingly receive the other end of thearmored sheath 32. The medial portion of the fitting 42 includes aradially projecting, locking flange 44. The fitting 42, theadjustingbolt 41 and the anchor unit 20 are so interconnected thatthreading the bolt 41 into the anchor unit 20 causes the fitting 42 andits boss 43 to be drawn toward the anchor unit 20.

It is preferred that the conductor 19 not be tensioned. By looselythreading the conductor 19 through the armored sheath 32 and forming aloop or bend 19a therein within the cavity of the anchor unit 20, aconnector configuration is established wherein little vibration istransmitted to the conductor lead which could eventually cause anelectrical failure.

A tubular braided sheath 50 of stainless steel having a plurality ofdouble-stranded interwoven helical coils 51 is firmly connected at itsends to the bosses 30 and 43 of the cap 11 and the fitting 42 of thestretching assembly 40 as by swaged sleeves 52 and 53. While the braidedsheath 50 may be joined to the boss 30 of the cap 11 by any desiredmethod, the preferred embodiment includes a thin polyurethane sheath 54which extends along the periphery of the boss 30 and which provides aseat into which the strands 51 of the braided sheath 50, which have beenbent over the flange 31, may be imbedded by the swaged sleeve 52.Another desirable method (not shown) of swaging the braided sheath 50 tothe boss 43 of the stretching assembly 40 contemplates the use of a pairof swaged sleeves made of materials having differing shrink rates sothat the inner sleeve made of a material such as plastic is swageddirectly to the boss 43 and provides the seat into which the strands 51may be imbedded by the overlying swaging sleeve.

The length of the braided sheath 50 relative to the length of thearmored sheath 32 is chosen so that in the particular installation thesubstantially untensioned sheath 50 assumes the greater diameteredprofile, generally indicated in exaggeration by dotted lines in Flg. 1,when the coupling 12 is unthreaded or the assembly 40 is adjusted tohave its greatest integral length. For installing the connector in aparticular rack, the assembly 40 is adapted for a sufficient initialreduction in length when the cap 11 has been firmly seated against thecartridge 17 so that the braided sheath 50 can be longitudinallystretched and reduced in diameter so that the helical strands 51 arestretched and tensioned to firmly grip the underlying periphery of thearmored sheath 32 and form therewith a conduit of desired rigidity. Theboss 43 is long enough so that the end of the armored sheath 32 remainswithin the bore 43a after the assembly 40 has been shortened to causethe braided sheath 50 to be necked down for tightly gripping theunderlying armored sheath 32. Thereby, a substantially rigid conduit maybe formed which can withstand the buffeting effects of air turbulence.At any time thereafter, the stiffness of the conduit may be relaxed byloosening the coupling 12 to untension the braided sheath 50. When thebreech cap 11 is disconnected from the barrel 13, the armored sheath 32may be flexed or bent to facilitate extracting the spent cartridge 17and loading another cartridge 17. Further adjustment of the assembly 40is usually unnecessary unless the coupling 12 is unable to sufficientlystretch the sheath 50.

Referring to FIG. 2, the armored sheath 32 is fonned from a helicallycoiled strip 61 having an inwardly depending tongue 62 which interlockswith a trough 63 inwardly depending from the confronting edge of theadjacent turn of the strip 61. Since the strands 51 of the braidedsheath 50 tightly grip the periphery of the coiled strip 61 when thestretching assembly 40 has been tightened, flexure or bending of theconnector 10 is inhibited. Also, when the braided sheath 50 is stretchedto radially compress the armored sheath 32, the tongue 62 tends to moreclosely engage the trough 63 and resist longitudinal sliding movementcharacteristically present when the armored sheath 32 is bent. Thearmored sheath 32 also includes a flexible plastic liner 64 whichfacilitates conductor insertion and protects the conductor 19 fromdamage by the sheath 32.

Referring again to FIG. 1, the head of the adjusting bolt 41 has aplurality of longitudinal slots such as 414 formed therein, any one ofwhich may be longitudinally registered with keying slots 20a and 44aformed in the anchor unit 20 and the locking flange 44 of the fitting42. An elongated key 70 is held in locking position by a pair ofbifurcated spring clips 71 and 72 spaced to be arranged on oppositesides of the head of the bolt 41 for clipping engagement of the shanksof the fitting 42 and the bolt 41. The key 70 is positioned to preventrotation of the adjusting bolt 41 once the desired degree oflongitudinal stretching of the braided sheath 50 has been imposed. Asnapon plastic cover 80 functions to streamline the connectorconfiguration, reducing the causation of turbulence, and to protect thestretching assembly 40 from the accumulation of dirt and ice which couldimpair its operation.

Referring to FIG. 3, the stainless steel ground contact pins arefabricated from flanged, cylindrical spring pins made of about two turnsof spirally wound rectangles of spring steel. As shown in FIG. 4, thepiercing point 91 of the pin 15 has been formed by obliquely truncatinga cylindrical pin as by cutting or grinding to form an elliptical pinterminus lying in a plane extending obliquely of the longitudinal axis Aof the pin 15. It has been found that, as shown in FIG. 5, when the pine15 is being forced into the aluminum casing of the cartridge 17 bythreading the coupling 12 onto the barrel 13 to seat the plate 14against the cartridge 17, the laminated walls of the pinpoint 91 tend toslightly diverge outwardly of the pin axis A and be forced obliquelyinto the aluminum casing. The furthest projecting portion of the point91 is deflected outwardly the greatest degree. The above-described pinconfiguration not only provides an excellent electrical contact with thecartridge 17 but also facilitates spent cartridge extraction in that, asthe uncoupled breech cap 11 is withdrawn from operative position, thepoints of the pins 15 tend to continue to grip the cartridge 17 andextract it from the barrel 13.

Several factors influence the design of the pins 15. For example, it hasbeen discovered that the distance that the points of the stainless steelspring pins 15 project beyond the plate 14 should be abouteighteen-thousandths of an inch when three ground contact pins having 1/16-inch diameters are to pierce an aluminum cartridge casing. Longerpoint projections prevent complete pin penetration and leave a gapbetween the plate 14 and the cartridge which can cause the pins 15 to besubjected upon detonation to sufficient cartridge kickback to stress thepins 15 beyond their elastic limits and impair the reuse of the cap 11and connector 10. It has been found that when the projecting ends of thepins 15 are too blunt, e.g., define a plane substantially normal to thepin axis, the pins will not pierce the aluminum cartridge casing asufficient degree for gripping engagement. On the other hand, if thepoints 91 are too sharp, e.g., in the above specific example, define aplane which is about 30-oblique to the pin axis A, seating the cap 11 onthe barrel 13 and tightening the coupling 12 causes the material in thepoints 91 to be stressed beyond its elastic limit, thereby causingpinpoint splaying and impairing reuse of the connector 10. While 45points usually have been found to be satisfactory for three I/ 16-inchdiametered pins used to pierce aluminum, a more blunt point such as onedefining a plane which is about 60 oblique to the pin axis A ispreferred in order to maintain a good electrical conduction path and toassure the feature of ability to extract spent aluminum cartridges. Whenthe spent cartridge 17 is disengaged from the pins 15, the pinpoints 91spring back to their normal orientation and are ready for reuse.

Another factor to be considered in designing reusable pins 15 is theperipheral location along the point 91 of the projected end of the outerlongitudinally extending wound rectangle edge 92. When the end of theedge 92 lies along the furthermost projecting half of the point 91, thepinpoint material tends to be stressed beyond its elastic limit uponbeing forced into a cartridge casing and, consequently, tends to bepermanently deformed. Permanent pinpoint splaying can be avoided bylocating the edge 92 in the other half of the pin 15 which projects theleast. Thus, the portion of the point 91 being forced into the casingwhich will undergo the greatest deflection from the longitudinal axisgenerally maintains the cross-sectional configuration of an unbrokendouble-layered elliptical arch during the piercing process. Since thematerial of the portion being inserted is more uniformly stressed, pointdeformation within the elastic limits of the material is better assured.I

It is preferred that the edge 92 be peripherally located halfway betweenthe longitudinal locations of the greatest and least point projections,i.e., that the length of the edge 92 be equal to the average length ofthe pin. This configuration facilitates mass production of the pins 15by enabling the use of a pair of jigs having at one end contiguous,coplanar edges slanted at the desired angle for the points 91 and havinga plurality of opposed semicylindrical bores extending normal to theslanted edge for receiving a plurality of unfinished pins 15. The edges92 of the pins 15 may be easily indexed into alignment with thelongitudinal boundaries of the bores in one of the jigs prior topositioning the mating jig. The proper peripheral location of the edge92 is thereby assured for each pin 15.

The invention provides an electrical connector 10 of greatly improveddesign which vastly increases the reliability of the bomb rack in that agood electrical connection between the cartridge 17 and the signalsource via the receptacle 23 is con-. tinually assured. Vibrationincident to in-flight conditions does not tend to cause failure of theelectrical interconnection between the cartridge 17 and the signalsource in that the ground contact pins 15 engage or grip the cartridgecasing with springlike action and in that the conductor 19 does not tendto vibrate and remains in an untensioned state, preserving theconduction path to the primary and ground contacts 15 and 16. Theflexible armored sheath 32 and the tensioned braided sheath 50 coact toform a substantially rigid conduit through which the conductor 19 isloosely threaded. The relaxable conduit formed thereby resists buffetingand vibration stimulated by air turbulence which could cause severanceof the conductor 19 or other failure of the connector 10.

It is contemplated, of course, that other known plug configurations notshown should be utilized. For example, the plug 32 could be mounted ontheend of a conduit rigidly secured to the frame which threadablyreceives a coupling member connected to the plug 21. It is furthercontemplated that the connector could include thermal insulation linersextending along the length of the armored sheath 32 for preventingpossible melting of the shield and lead of the conductor 19 in thepresence of rocket blasts.

lt should be understood, of course, that the foregoing disclosurerelates only to a preferred embodiment of the invention and thatnumerous modifications or alterations may be made without departing fromthe spirit and scope of the invention as set forth in the appendedclaims.

We claim:

1. A conduit of adjustable stiffness comprising:

a helically coiled strip forming an elongated flexible tube whoseresistance to flexure increases when subjected to radial compression;

an elongated tubular sheath whose transverse dimension changes as afunction of change in its length, said tube being arranged inside saidsheath and having confronting boundaries for providing surface contactbetween said tube and said sheath;

anchor means connected to one end of said sheath;

a threaded coupling having a protruding boss secured to the other end ofsaid sheath and an axial bore slidably receiving the adjacent end ofsaid tube;

a threaded fitting threadably engaging said coupling for changing thelength of said sheath in a direction to cause said confrontingboundaries to engage each other exerting radial compression on said tubeand reducing the flexibility thereof;

an anchor member having a threaded chamber receiving said fitting;

said coupling, said fitting and said anchor member each having slots ofwhich are registrable with each other;

a key engageable with said slots in registration preventing rotation ofsaid coupling and said fitting; and

means for retaining said key in said registered slots.

2. A conduit according to claim 1 further comprising:

an electrical conductor freely carried within said tube; and

said coupling, said fitting and said anchor member defining a channelthrough which said conductor extends, one end of said conductor forminga terminal in said anchor member.

1. A conduit of adjustable stiffness comprising: a helically coiledstrip forming an elongated flexible tube whose resistance to flexureincreases when subjected to radial compression; an elongated tubularsheath whose transverse dimension changes as a function of change in itslength, said tube being arranged inside said sheath and havingconfronting boundaries for providing surface contact between said tubeand said sheath; anchor means connected to one end of said sheath; athreaded coupling having a protruding boss secured to the other end ofsaid sheath and an axial bore slidably receiving the adjacent end ofsaid tube; a threaded fitting threadably engaging said coupling forchanging the length of said sheath in a direction to cause saidconfronting boundaries to engage each other exerting radial compressionon said tube and reducing the flexibility thereof; an anchor memberhaving a threaded chamber receiving said fitting; said coupling, saidfitting and said anchor member each having slots of which areregistrable with each other; a key engageable with said slots inregistration preventing rotation of said coupling and said fitting; andmeans for retaining said key in said registered slots.
 2. A conduitaccording to claim 1 further comprising: an electrical conductor freelycarried within said tube; and said coupling, said fitting and saidanchor member defining a channel through which said conductor extends,one end of said conductor forming a terminal in said anchor member.